This proposal focuses on the neuroendocrine mechanisms determining social and reproductive behaviors among vertebrates. Across different classes of vertebrates, the neuropeptide arginine vasotocin (AVT), as well as its mammalian homologue arginine vasopressin (AVP), play a key role in the regulation of complex male social behaviors such as aggression, courtship, and vocalizations associated with these behaviors. Many studies indicate that AVT/AVP's role in modulating these behaviors is a function of the social system of the species in question, however there is evidence that individual status within a social system also plays a part in determining the directionality of AVT/AVP's influences, i.e. either facilitating or inhibiting behavior. Few studies focus on the interaction between environment and hormone function in the expression of individual behavior. Among beaugregory damselfish, males exhibit different levels of aggression and courtship based upon their territory quality. The overall goal of this proposal is to identify how AVT- interacts with an individual's ecology (i.e. territory quality) to modulate aggression, courtship, and the vocalizations associated with these behaviors. [unreadable] [unreadable]